Silicon is employed for a public solar cell. While conversion efficiency is decreased in order of single-crystalline silicon, polycrystalline silicon and amorphous silicon, the cost is reduced in the aforementioned order to readily implement a larger area. Among these, amorphous silicon, which can be deposited from a raw material of SiH4 on a substrate of glass, plastic or metal by CVD (Chemical Vapor Deposition), is at a low cost and can be readily increased in area. The conversion efficiency is about 12% at the maximum.
As to single-crystalline silicon, an ingot having a diameter of 150 mm (6 inches) or 200 mm (8 inches) is manufactured by the CZ (Czochralski) method and can be increased in size, and the conversion efficiency thereof can exceed 15%.
As to polycrystalline silicon, a method of solidifying/growing the same from a liquid phase or a method of depositing the same from a vapor phase is researched. While polycrystalline silicon can be readily increased in area similarly to amorphous silicon, the conversion efficiency thereof is on an intermediate position between those of single-crystalline silicon and amorphous silicon.
Each of the aforementioned various types of silicon manufacturing methods increases the area, improves of the conversion efficiency and reduces the manufacturing cost. However, the unit generating cost thereof is rather expensive as compared with the present large-scale power generation system such as nuclear power generation or thermal power generation, and the manufacturing cost must be reduced.